-16m^2-48m^4+24m^6
= 24m^6-48m^4-16m^2
=8m^2(3m^4-6m^2-2)
2、25x^2-16y^2
=(5x+4y)(5x-4y)
3、a^4b^4-c^4
=(a^2b^2+c^2)(a^2b^2-c^2)
=(a^2b^2+c^2)(ab-c)(ab+c)
4、（xy-x^2）^3-x^3（y-x）
=[x(y-x)]^3-x^3(y-x)
=x^3(y-x)^3-x^3(y-x)
=x^3(y-x)[(y-x)^2-1]
=x^3(y-x)[(x-y)^2-1]
=x^3(y-x)(x-y-1)(x-y+1)